Films using blends of polypropylene and polyisobutylene

ABSTRACT

This invention teaches using blends of polyisobutylene and polypropylene copolymer in the formation of single layer films and multiple layer sheet materials. The films and sheet materials are useful as flexible packaging materials. The multiple layer sheet materials may be entirely polymeric or may include layers having non-polymeric components, such as metal. The blends of polyisobutylene and polypropylene copolymer unexpectedly have the capability of being extruded through a slot die to form a film having a functionally useful mixture of its components. Thus the invention further includes methods of forming film-like layers of the blends of polyisobutylene and polypropylene copolymer.

This is a division of application Ser. No. 07/207,369, filed Jun. 13,1988, now U.S. Pat. No. 5,006,384 which in turn is a division ofapplication Ser. No. 144,652, filed Jan. 11, 1988, now U.S. Pat. No.4,892,911, which in turn is a continuation of application Ser. No.06/803,029, filed Nov. 29, 1985 now abandoned.

This invention pertains to packaging. It pertains in some respects tocompositions of matter and single layer polymeric films made therefrom,and in other respects to multiple layer sheet materials and packagesmade therefrom. The sheet materials may be entirely polymeric, or theymay include non-polymeric components. The multiple layer materials maybe flexible, or relatively rigid. The invention also pertains toprocesses for making packaging materials. This invention is especiallyconcerned with packaging sheet materials which are formed into packages.

Various packaging applications wherein a product is packaged in a heatsealable sheet material require that the finished package to be able towithstand substantial abuse, such as in shipping and handling. In somepackaging applications, the package, including the packaging materialsand the product being packaged, may be subject to certain processtreatments either during or after the filling and sealing of thepackage. One such application is retortable packages, where the packageis subjected to sterilizing conditions of typically about 250° F., andappropriate respective pressures for steam sterilization, typically forperiods of 30-60 minutes, but sometimes as little as 10 minutes isacceptable.

A multiplicity of packaging materials have been developed for use inheat seal-type packaging. While many of these packaging materials haveexperienced a degree of success, there remain problems in packages whichare subject to certain abuses related to their use. Particularly,packages containing liquid products experience hydraulic pressuresexerted by the liquid product when they receive physical shocks such aswhen dropped, or moved in a rough manner. Where the shock issufficiently strong, the heat seals may break as a result. And whilecertain sheet structures are in conventional use, it is desirable tomake improved economical sheet structures which can be used to make evenstronger packages, and particularly, stronger package sealant layers andseals, to further reduce the incidence of failure of the filled andsealed package. Packaging materials which have been subjected to hightemperature processing are particularly susceptible to breakage of thepackage seals.

Particularly referring, now, to package which are subjected to thermalprocessing, as in retort processing typically at about 250° F., sealantlayers are known to be made of polypropylene, as in U.S. Pat. No.4,190,477. While polypropylene sealant layers are functionally capableof withstanding the processing conditions, the heat seals, as measuredafter processing, could desirably be stronger.

It is an object of this invention to provide novel packaging sheetmaterials.

It is another object of the invention to provide novel multiple layersheet materials having improved capability to withstand physical shockswhen formed into flexible heat sealed packages filled with liquid, andpackages made from those sheet materials.

It is still another object to provide such novel sheet materials havinggood barrier to transmission of gases or moisture into or out of thepackage.

It is yet another object to provide novel sheet materials capable ofwithstanding substantial physical shocks when formed into flexible heatsealed packages filled with liquid; the packages having good barrier totransmission of gases or moisture; and the packages having sufficientoptical clarity through the sheet material to enable visual inspectionof the package contents; and packages made from those sheet materials.

Further objects are in processes for making the improved sheet materialsof the invention, and the packages made therefrom.

SUMMARY OF THE INVENTION

The invention is seen to be embodied in an unsupported polymeric filmwhich is a blend of about 10% to 65% by weight polyisobutylene andconversely about 90% to 35% by weight of polypropylene copolymer. Thepolypropylene is preferably a copolymer having about 70 to about 98 molepercent propylene moieties and conversely about 30 to about 2 molepercent ethylene moieties. Preferred films have a blend composition of20% to 40% by weight polyisobutylene and 80% to 60% by weightpolypropylene copolymer. It is also preferred that the polypropylenecopolymer is 92 to 98 mole percent propylene moieties and conversely 2to 8 mole percent ethylene moieties.

The preferred process of making the films includes the steps ofextruding the blend through a die, and cooling the extruded blend toform a solid. In the process of making the films of the invention, it isentirely acceptable to form a particulate blend of the polypropylenecopolymer and the polyisobutylene, where the particles in the blendgenerally have a size greater than 0.5 micron diameter, and to processthe blend by extruding it through a die, followed by cooling theextruded blend to form a solid.

The invention is also embodied in multiple layer sheet materials. In onesuch sheet material, a first polypropylene-based layer having twoopposing surfaces is composed of a polypropylene based of the invention.The polypropylene used in the blend is preferably a copolymer having 70to 98 mole percent propylene moieties and conversely 30 to 2 molepercent ethylene moieties. A second layer of a metal foil is affixed onone of the surfaces of the first layer. The first layer is preferably60% to 80% by weight polypropylene copolymer and 40% to 20% by weightpolyisobutylene. In more preferred forms, the polpropylene copolymer inthe first layer is 92 to 98 mole percent propylene moieties andconversely 2 to 8 mole percent ethylene moieties. In some embodiments ofthese sheet materials, the first layer is adhered to the second layer bya polymeric adhesive, the adhesive being between the first and secondlayers. There are also embodiments of the invention where additionallayers are used. In one such embodiment, an abuse resistant layer isadhered to the second surface of the second layer of metal foil by anadhesive layer, namely that surface which is opposite the surface whichis adhered to the first blend layer. Exemplary materials for use in theabuse resistant layer are oriented polyamides, oriented polyesters andoriented polypropylenes.

In one family of embodiments, in which the invention is exemplified bythe multiple layer sheet material having a first layer of the blend ofpolypropylene copolymer and polyisobutylene and a second layer of metalfoil, it is convenient to adhere the first layer to the second layer byuse of an adhesive layer of polypropylene copolymer therebetween. Insome cases, it is expedient to include a primer between the second layerand the polypropylene copolymer layer. Preferred primer has carboxymoieties. Further, the layer of polypropylene copolymer includes carboxymoieties in some embodiments.

In another family of embodiments, the invention is exemplified by amultiple layer sheet material having barrier properties provided bypolymeric materials. A first layer is of the blend of polypropylenecopolymer and polyisobutylene. A second layer of a polyamide having twoopposing surfaces is adhered, on one of its surfaces to one surface ofthe first layer. A third barrier layer having two opposing surfaces isadhered on one of its surfaces to the other surface of the second layerof polyamide. Preferred composition for the third layer is about 50% toabout 90% by weight of a first material which is vinyl alcohol copolymerand conversely about 50% to about 10% by weight of a second materialwhich is a polymer compatible with ethylene vinyl alcohol copolymer inblend composition. "Compatible" means the capability for polymers to beextruded in blend composition. A fourth layer of a polyamide, having twoopposing surfaces, is adhered in one of its said surfaces to the othersurface of the third layer. In some preferred versions of this family ofembodiments, the second material is polyetheramide block copolymer. Forthose structures desiring higher levels of adhesion, a layer of anadhesive polymer may be interposed between the first and second layers.Finally, a fifth layer of biaxially oriented nylon may be adhered to theother surface of the fourth layer.

Within the family of embodiments having barrier properties provided bypolymeric materials, one sub-family uses as the barrier layer a secondlayer comprised of vinylidene chloride copolymer. The second layer hastwo opposing surfaces and is adhered to the first layer on one of itssurfaces by a third layer of an adhesive therebetween. A fourth layer ofa polyamide may be adhered to the other surface of the second layer by afifth layer of an adhesive therebetween.

The various films and sheet materials of the invention are susceptibleto being made into packages by the formation of seals about an enclosedarea, to effect the closing and sealing of the packages.

The processes for making films and sheet materials of the inventioninclude the formation of blends of polypropylene copolymer andpolyisobutylene using particles generally larger than 0.5 micron. Theparticulate blend is then extruded or coextruded to form the films ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a single layer film of this invention.

FIG. 2 is a cross-section of a two-layer sheet material of theinvention, using a metal foil layer.

FIG. 3 is a cross-section of a three-layer sheet material of theinvention, using a metal foil layer.

FIG. 4 is a cross-section of a six-layer sheet material of theinvention, using a metal foil layer.

FIG. 5 is a cross-section of a seven-layer sheet material of theinvention, and wherein the composite sheet structure may have opticalclarity for visual inspection through the sheet material.

FIG. 6 is a cross-section of a five-layer sheet material of theinvention, and wherein the composite sheet material may have opticalclarity for visual inspection through the sheet material.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is first seen in a single layer 12 of film of generallyindefinite length. A cross-section of a piece of such a film is seen inFIG. 1. The film is a blend of about 10% by weight to about 65% byweight polyisobutylene and conversely about 90% to about 35% weightpolypropylene copolymer. The polypropylene copolymer is especiallyselected to contain about 70 to about 98 mole percent propylene moietiesand conversely about 30 to about 2 mole percent ethylene moieties. Theoverall blend composition has at least about 1.8 mole percent ethylene.

FIGS. 2 and 3 show the invention as it is used in simple multiple layersheet structure wherein a layer of metal foil is joined to the blendlayer. In the structure of FIG. 2, the foil layer 14 is adhered directlyto the blend layer 12 without the use of intervening adhesives. In FIG.3, a third adhesive layer 16 is used to promote improved adhesionbetween layers 12 and 14.

FIG. 4 illustrates a more complex form of sheet structures of theinvention which include therein a layer of metal foil. The FIG. 4structure includes the same layers 12, 14, and 16 as in FIG. 3. Inaddition, its shows an optional primer layer 18 between layers 14 and16. An abuse resistant layer 22 is adhered to foil layer 14 by anintervening layer 20.

FIG. 5 illustrates a multiple layer polymeric barrier film of theinvention. In this embodiment, an adhesive layer 30 is adhering a nylonlayer 24 to the blend layer 12. A barrier layer 26 includes ethylenevinyl alcohol copolymer (EVOH) for reducing transmission of gasesthrough the film. Nylon layer 28 is adjacent EVOH layer 26. Optionalabuse resistant layer 22 is adhered to nylon layer 28 for the purpose ofproviding further physical protection of the overall film.

FIG. 6 shows another embodiment of a multiple layer barrier film whichuses, as a barrier, a layer of vinylidene chloride copolymer. In thisillustrated embodiment, layer 12 is the blend layer, layer 36 is abarrier layer of saran and layer 40 is a layer of nylon. Interveninglayers 34 and 38 are adhesives functional to hold the respective layersto each other, and functional to hold the structure together as a whole.

It is entirely possible to incorporate the invention, including any ofthe embodiments herein, as a substructure, into other structures.Similarly, additional layers may be added to the structures disclosedherein without departing from the contemplated scope and intent of theinvention.

THE BLENDS

The blends of layer 12 have two essential components. The firstcomponent is polyisobutylene. The second component is polypropylenecopolymer. The inventor has found that it is critical that thepolypropylene component contain some ethylene in order to impart to theoverall blend composition the desired degree of shock resistance. Thepolypropylene component of the blend may be all copolymer or a blend ofcopolymer and homopolymer. The recitation of polypropylene copolymerhereinafter includes blends of copolymer and polypropylene homopolymer.While blends of polypropylene and polyisobutylene may be made usingpolypropylene homopolymer, and heat sealable sheet materials may be madetherefrom, those sheet materials exhibit less shock resistance than thestructures of the invention.

With the inclusion of as little as about 1.8 mole percent ethylene inthe propylene component, improvement is seen in the shock resistance ofpackages made therefrom. As the amount of ethylene is increased, theshock resistance generally improves, and up to about 30 mole percentethylene may be used. As the amount of ethylene is increased, thecapability of the blend to withstand heat (heat resistance) isdecreased. At the higher fractions of ethylene content, the heatresistance is less than desired for some uses. Thus, for those uses inwhich the packaging sheet material is required to have high heatresistance, an ethylene content of about 2 to about 8 mole percent ispreferred in the polypropylene copolymer, and the presence of at leastabout 2 mole percent is necessary as a condition in this invention.

Since the various polymeric layers in the invention are intended to beused primarily in extrusion process through a slot die, it issignificant that each material be obtained in such a form as is readilyconducive to its use in the extrusion process, and that it be obtainedat economically favorable cost. As is well know, polyisobutylene iscommercially supplied in the form of large blocks, or bales. In order toprepare polyisobutylene for extrusion, it is thus necessary to convertit to another form. Conversion of polyisobutylene into pellets is notknown to have been done. Its rubbery physical characteristics mayprevent its being prepared in pellet form, as is, for example, thepolypropylene copolymer. The polyisobutylene may be melted from the baleand blended with a polypropylene, either copolymer or homopolymer, toform a master batch of a blend of polyisobutylene and polypropylene. Theso-formed master batch may be formed into conventional pellets for usein extruding the blends of this invention to form layers. In making thefinal blends for use herein, the master batch pellets may be blendedwith additional polypropylene, which must include copolymer, to make thedesired blend ratio of polyisobutylene to polypropylene.

The preparation of a master batch by melt mixing togetherpolyisobutylene with polypropylene copolymer to form a blend is seen assignificant to the desired objective of economically forming a film froma blend of polyisobutylene and polypropylene copolymer. While a masterbatch may be so blended as to yield a blend composition as desired forforming a film, it is usually preferred to form a master batch having alower polypropylene content and to form it into conventional pelletssuitable for extrusion. This minimizes both the cost of making themaster batch and the thermal exposure of the polypropylene. The finaldesired blend composition is economically achieved by dry blending apre-determined amount of the master batch pellets with a pre-determinedamount of polypropylene copolymer pellets and extruding the mixture,thus achieving the desired final blend composition in the extrudedlayer.

In typical formation of blend layers in the invention, a master batch iscompounded by melting polyisobutylene and mixing into the melt an amountof polypropylene, preferably pellets, sufficient to make a blend of 65%by weight polyisobutylene and 35% polypropylene. The blend is heatedsufficiently to melt all the polypropylene, and is mixed thoroughly. Themelted master batch blend is then formed into pellets and cooled. Information of the final composition, pellets of the master batch aremixed with pellets of a selected polypropylene copolymer. A typicalblend ratio with the above-mentioned master batch is 42% by weightpolypropylene copolymer and 58% by weight master batch. The finalcomposition is thus 37.7% polyisobutylene and 62.3% polypropylene,including the polypropylene in the master batch. Where the selectedpolypropylene copolymer is, for example 4% ethylene, and it is used forboth the blend component and in the master batch, the overall content ofthe blend is 2.5% ethylene.

The blends used in the invention may be compounded in the melted mixtureof the master batch in the desired final blend ration to be extruded.When the desired final blend is thus made as the master batch, thecompounded pellets may be extruded without further addition, as ofpellets of polypropylene copolymer. While this process, which eliminatesa step of dry blending, does produce acceptable blends for use in theinvention, where the at least 1.8 percent ethylene is present in theform of polypropylene copolymer, the cost of processing the additionalpolypropylene in the melt compounding operation usually exceeds the costof the eliminated dry blending step. Thus, the two step process isusually preferred in preparing material for extrusion processing.

THE MULTIPLE LAYER MATERIALS

The blends described above have preferred utility when used withadditional layers. The additional layers may be polymeric ornon-polymeric. Conventional additives and fillers may be used. Normalamounts of additives and modifiers may be included in the blend layer12.

In the formation of the sheet material of FIG. 2, it is desirable toselect, for inclusion in the blend composition of layer 12, a polymerhaving carboxy modifications thereto, to enhance adhesion between blendlayer 12 and metal foil layer 14. Carboxy modified propylene polymersare available from Mitsui Company, Japan as "QF" series polymers.

Another way of obtaining adhesion between layers 12 and 14 is through aseparate layer of adhesive as at 16 of FIG. 3. A relatively thin layerof adhesive may be used, such as 2 to 3 pounds per 3000 square footream. Various adhesives are conventionally know for use in adhesion tometal foil, as in layer 14. Exemplary of these adhesives, for use inlayer 16 are the curing type polyester urethane adhesives. One suchacceptable adhesive is available from Morton Chemical Company as Adcote506-40 . The adhesive layer 16 may be in direct contact with the foillayer 14, or a primer layer, as at 13 in FIG. 4 may be interposedbetween foil layer 14 and adhesive layer 16. The primer layer 18, whenused, is only of sufficient thickness to ensure its continuity. Asuitable primer is Morprime from Morton Chemical Company, a modifiedpolypropylene provided in a liquid carrier. The liquid primer isconveniently applied to the surface of the metal foil layer 14, and theliquid removed by evaporation.

The primer may then be cured by application of heat. Finally, theadhesive layer 16 and blend layer 12 are applied to the primed foillayer 14, preferably with pressure to promote adhesion between theseveral and respective layers in the composite structure of layers 12,14, 16 and 18.

In completion of the structure shown in FIG. 4, an abuse resistant layer22 may be adhered to the other surface of foil layer 14 by use of anadhesive layer 20. Materials conventionally known for their abuseresistance properties, such as oriented nylon, oriented polyester andoriented polypropylene, are satisfactory. Conventional adhesives areknown for adhering the abuse resistant materials to metal foil. Theadhesive selected will, of course, depend on the selection of the abuseresistant layer. In one such combination, a layer 22 of biaxiallyoriented nylon is adhered to foil layer 14 by a curing-type polyesterurethane adhesive.

The metal foil layer 14 in the embodiments of FIGS. 2, 3, and 4 providesexcellent barrier to transmissions of gases and light through the sheetstructure. There are, however, applications for sheet materials wherethe use of metal foil is not desirable. FIGS. 5 and 6 illustratemultiple layer films having polymeric layers that provide barrier togaseous transmissions through the films.

In the structures of FIG. 5, layer 12 is thepolyisobutylene-polypropylene copolymer blend. Layers 24 and 28 arenylon. Layer 26 is EVOH or a blend of EVOH. Layer 30 is an adhesiveeffective to bond layers 12 and 24 into the structure. Layer 22 is anabuse resistant layer, adhered to nylon layer 28, optionally through useof an adhesive layer 32. Layers 24 and 28 preferably contain nylon 6 andmay contain other polyamide polymers. Other nylons may be substitutedfor nylon 6 where heat resistance is not critical. While layers 26 maybe EVOH, a preferred composition for layer 26 is a blend of 50% byweight to 90% weight of a first polymer of EVOH and 50% by weight to 10%by weight of a second polymer compatible with EVOH in blend composition.The second polymer may be selected with a substantial degree of freedom,and initial determination of suitability of any given polymer isdependent primarily on its compatibility in blend composition with EVHO.Among the suitable choices for the second polymer are ethylene ethylacrylate, ethylene acrylic acid, linear low density polyethylene,ionomer, anhydride modified low density polyrthylene, anhydride modifiedmedium density polyethylene, anhydride modified high densitypolyethylene, nylon, and polyetheramide block copolymer. The selectionof the specific material for the second polymer will, of course, dependon the composition and use of the overall multiple layer structure. Withthe disclosure herein, expedient selection of the second polymer can bemade by those of average skill in the art.

Adhesive layers 30 and 32 may conveniently be polyester urethane, andthe structure may conveniently be formed by adhesive laminationtechniques. In formation by adhesive lamination, three separatesubstructures may initially be formed. The first substructure is theblend layer 12 which is formed by extrusion as for the single layer filmof FIG. 1. the second substructure is the three layer substructure/nylon/EVOH/nylon/ of layers 24, 26, and 28. This three layersubstructure is conveniently formed by conventional coextrusion. Thethird substructure is the abuse resistant layer 22, which is typicallyformed by conventional extrusion and which is usually followed bymolecular orientation. After the three substructures are formed, theymay be combined by conventional lamination processes. They mayalternatively be combined by other processes such as extrusionlamination processes.

In another process for making multiple layer films as in FIG. 5, layers12, 30, 24, 26 and 28 may be coextruded as a first substructure. Layer22 is separately prepared as above. Layer 22 is joined to layer 28 byconventional method.

Another family of multiple layer structures of the invention isillustrated in FIG. 6. Layer 12 is the blend layer. Layer 36 is avinylidene chloride copolymer. Preferred copolymers for layer 36 arevinyl chloride-vinylidene chloride copolymers and vinylidene chloridemethylacrylate copolymers. Layer 40 is nylon. Layers 34 and 38 areadhesives which adhere together the several layers of the structure. Thestructure is typically formed by separately forming layers 12, 36 and 40by individual extrusion processes. The composite multiple layerstructure is then assembled by conventional combining process, such asadhesive lamination, extrusion lamination or the like.

Other combinations of conventional processes can be used to form thestructures of the invention, and will now be obvious to those skilled inthe art.

Sheet materials such as those illustrated in FIGS. 5 and 6 may be formedfrom materials, each of which offers substantial optical transparency.The finished sheet materials represented by FIGS. 5 and 6 also typicallyhave sufficient optical clarity through the sheet material to enablevisual inspection of the package contents. Other structures of theinvention which do not use opague materials such as metal foil, paper orfillers, also typically offer the same optical clarity.

Flexible packages, of the pouch type, may be made from any of the singleof multiple layer sheet materials of the invention using conventionalprocesses to form heat seals about an enclosed area defined by facingportions of the sheet material. The sheet materials may also be used incombination with other packaging structures. Sheet structures may, forexample, be used as lid materials for rigid trays formed from otherpackaging structure.

EXAMPLE 1

Pallets of polypropylene copolymer, containing 4% ethylene are mixedwith pellets of a master batch which consists of 65% polyisobutyleneconsists of 65% polyisobutylene and 35% polypropylene copolymer, wherethe polypropylene copolymer used in the master batch contains 4%ethylene. The mixture is 58% weight pellets of the master batch and 42%pellets of the polypropylene copolymer yielding a blend which is 37.7%polyisobutylene, 59.8% propylene and 2.5% ethylene. The mixture isextruded through a slot die to form a single layer film 4 mils thick.The so-prepared film is laminated to one surface of a layer of 35 gaugealuminum foil being using a polyester urethane adhesive. The othersurface of the foil is laminated to a layer of 60 gauge biaxiallyoriented nylon, using a polyester urethane adhesive.

EXAMPLE 2

A sheet structure is prepared as in EXAMPLE 1 except that thepolypropylene used to make the master batch is a homopolymer.

COMPARATIVE EXAMPLE 1

A sheet structure is prepared as in EXAMPLE 1 except that the layercomparable to the blend layer in EXAMPLE 1 is polypropylene copolymer,without any polyisobutylene.

COMPARATIVE EXAMPLE 2

A sheet structure is prepared as in EXAMPLE 2 except that thepolypropylene blended with the master batch is a homopolymer.

EXAMPLE 3

A single layer film is prepared for the blend layer as in EXAMPLE 1. Athree-layer substructure is prepared by coextruding an EVOH layer as acore layer with outer layers of nylon, to form a substructure of thenature of /nylon/EVOH/nylon/. The three-layer substructure is thenlaminated to the blend layer using a polyester urethane adhesive.

EXAMPLE 4

A five layer film is prepared by coextruding through a combining die astructure of /nylon/EVOH/nylon/adhesive/blend/. The blend layer is thesame mixture as was prepared by mixing pellets for extrusion inEXAPLE 1. The adhesive material is QF500X, for Mitsui Company, Japan. Inthe finished film, the blend layer is 4.0 mils thick. The EVOH layer is0.5 mil thick. The nylon layers are 0.25 mil thick. The adhesive isminimal thickness for continuity, about 0.1 mil.

EXAMPLE 5

A single layer film is prepared for the blend layer as in EXAMPLE 1. Theblend layer is laminated to one surface of a layer of biaxially orientedsaran using a polyester urethane adhesive having an aliphatic chaincatalyst. A layer of 60 gauge biaxially oriented nylon is laminated tothe other surface of the saran using the same polyester urethaneadhesive.

EXAMPLE 6

A multiple layer sheet material is made as in EXAMPLE 1 except that theratio of the mixture of pellets in the blend layer is 30% by weightpellets of the master batch and 70% pellets of the polypropylenecopolymer. The resulting blend composition is 19.5% polyisobutylene and80.5% polypropylene copolymer.

The sheet materials of EXAMPLE 1 and EXAMPLE 2 and Comparative Example 1are used to make heat sealed packages containing about 100 fl. oz. ofwater. The edge seals are 3/8 inch wide. The packages are then retortprocessed at 250° F. and about 25 psig pressure for 30 minutes. Theretort processed packages are cooled to room temperature. A test packageis then placed in a simulated shipping container. A flat, uniform weightis placed on top of the package; a 14 lb. weight to simulate stackingthe packages 3 high, or a 35 lb. weight to simulate stacking thepackages 6 high.

The shipping containers were then dropped onto a hard surface fromvarious heights at 6 inch intervals. Each package was subjected to onedrop from a selected height. After the drop, each package was inspectedfor weakening or failure as the seal area. In general, six drops weremade of six packages at each height reported. In some cases, the packageseals were substantially weakened, as evidenced by stretching, ornarrowing of the seal width through no leakage occured. These weakenedpackages were counted as failures. The results of all the tests are seenin Table 1.

                  TABLE 1                                                         ______________________________________                                        Sample    Drop Height Survived Without Package Failure                        Identification                                                                          14. lb. top load                                                                              35. lb. top load                                    ______________________________________                                        Example 1 all survive at 24 inches                                                                      all survive at 6 inches                             Example 2 all survive at 18 inches                                                                      all fail at 6 inches                                          60% fail at 24 inches                                                                           --                                                Comparative                                                                             all fail at 6 inches                                                                          all fail at 6 inches                                Example 1                                                                     ______________________________________                                    

The results show that the packages in EXAMPLE 1 and EXAMPLE 2 aresignificantly better than the packages of Comparative Example 1 whereinthe blend layer does not contain polyisobutylene. Further, packages ofEXAMPLE 1 tend to be somewhat better than those of EXAMPLE 2 wherein thepackages of EXAMPLE 2 contain more homopolymer polypropylene componentby virtue of the homopolymer in the master batch.

Thus it is seen that the invention provides novel sheet materials havingimproved capability to withstand physical shocks when formed intoflexible heat sealed packages filled with liquid, and packages made fromthose sheet materials.

It is further seen that the sheet materials and packages of theinvention provide good barrier to transmission of gases into or out ofthe package. Certain of the sheet materials and packages have goodoptical clarity through the sheet material, enabling visual inspectionof the contents.

Processes are also provided for making the improved sheet materials ofthe invention.

I claim:
 1. A multiple layer sheet material, comprising:(a) a firstpolypropylene-based layer having two opposing surfaces, said first layerbeing a blend of 35% to 90% by weight polypropylene copolymer andconversely 65% to 10% by weight polyisobutylene, said polypropylenecopolymer comprising 70 to 98 mole percent propylene moieties andconversely 30 to 2 mole percent ethylene moieties, the overallcomposition of said blend comprising at least about 1.8 mole percentethylene; and (b) a second layer of a metal foil affixed on one saidsurface of said first layer.
 2. multiple layer sheet material as inclaim 1 wherein said blend in said first layer comprises 60% to 80% byweight polypropylene copolymer and 40% to 20% by weight polyisobutylene.3. A multiple layer sheet material as in claim 1 wherein saidpolypropylene copolymer in said first layer comprises 92 to 98 molepercent propylene moieties and conversely 2 to 8 mole percent ethylenemoieties.
 4. A multiple layer sheet material as in claim 2 wherein saidpolypropylene copolymer in said first layer comprises 92 to 98 molepercent propylene moieties and conversely 2 to 8 mole percent ethylenemoieties.
 5. A multiple layer sheet material as in claim 1 wherein saidfirst layer is adhered to said second layer by a polymeric adhesive,said adhesive being between said first and second layers.
 6. A multiplelayer sheet material as in claim 2 wherein said first layer is adheredto said second layer by a polymeric adhesive, said adhesive beingbetween said first and second layers.
 7. A multiple layer sheet materialas in claim 5 wherein said second layer has two opposing surfaces, saidpolymeric adhesive being on one said surface and adhering said onesurface to said first layer, and wherein an abuse resistant layer isadhered to the other said surface of said second layer of metal foil byan adhesive layer.
 8. A multiple layer sheet material as in claim 7wherein said abuse resistant layer is biaxially oriented nylon.
 9. Amultiple layer sheet material as in claim 8 wherein said blend in saidfirst layer comprises 60% to 80% by weight polypropylene copolymer and40% to 20% by weight polyisobutylene.
 10. A multiple layer sheetmaterial as in claim 8 wherein said polypropylene copolymer in saidfirst layer comprises 92 to 98 mole percent propylene moieties andconversely 2 to 8 mole percent ethylene moieties.
 11. A multiple layersheet material as in claim 9 wherein said polypropylene copolymer insaid first layer comprises 92 to 98 mole percent propylene moieties andconversely 2 to 8 mole percent ethylene moieties.
 12. A multiple layersheet material as in claim 1 wherein said first layer is adhered to saidsecond layer by a layer of polypropylene copolymer therebetween.
 13. Amultiple layer sheet material as in claim 12 and including a primerbetween said second layer and said polypropylene copolymer layer, saidprimer comprising carboxy moieties.
 14. A multiple layer sheet materialas in claim 12 and wherein said second layer has two opposing surfaces,said polypropylene copolymer layer being on one said surface andadhering said one surface to said first layer, and wherein an abuseresistant layer is adhered to the other said surface of said secondlayer of metal foil.
 15. A multiple layer sheet material as in claim 13wherein said second layer has two opposing surfaces, said polypropylenecopolymer layer being on one said surface and adhering said one surfaceto said first layer, and wherein an abuse resistant layer is adhered tothe other said surface of said second layer of metal foil.
 16. Amultiple layer sheet material as in claim 14 wherein said abuseresistant layer is biaxially oreinted nylon.
 17. A multiple layer sheetmaterial as in claim 15 wherein said abuse resistant layer is biaxiallyoreinted nylon.
 18. A multiple layer sheet material as in claim 12wherein said layer of polypropylene copolymer includes carboxy moieties.19. A package made from sheet material of claim
 1. 20. A package madefrom sheet material of claim
 4. 21. A package made from sheet materialof claim
 5. 22. A package made from sheet material of claim
 6. 23. Apackage made from sheet material of claim
 7. 24. A package made fromsheet material of claim
 11. 25. A package made from sheet material ofclaim
 12. 26. A package made from sheet material of claim
 13. 27. Apackage made from sheet material of claim
 15. 28. A package made fromsheet material of claim 18.